A seatbelt buckle is described in EP 0 212 507 B1. In seatbelt buckles of this type, it is important to design them as shockproof. For example, when the seatbelt buckle is accelerated, as part of a tensioning action, and then abruptly decelerated at the end of the tensioning path, the forces acting in the direction of motion of the slide button caused by acceleration, may actuate the slide button into the decelerated buckle housing due to its own mass inertia and thereby opening the buckle. As per an example described in EP 0 212 507 B1, an inertial mass is arranged in the buckle housing so that it slides linearly in the direction of motion of the slide button. Because of the motion relative to the housing caused by the forces of acceleration, the inertial mass pivots a two-arm coupling lever rotatably mounted in the housing in such a manner that the free arm of the coupling lever intervenes in the motion path of the slide button. This thus prevents an insertion and opening movement of the slide button acting in the same direction as the motion of the inertial mass.
However, the seatbelt buckle in accordance with the prior art may be associated with the disadvantage that the separate arrangement of the linearly moving inertial mass, along with its associated guide and support in the housing of the seatbelt buckle, has a large space requirement so that the buckle body must be designed to be large in size. The known solution additionally means increased expense for manufacture and assembly. Finally, the inertial forces of the inertial mass must be matched to the inertial force acting on the slide button very exactly so that the coupling lever, when triggered, will pivot into the motion path of the slide button in a timely manner before the slide button is in motion.